Blades are normally sold by a number such as Grade 7, Number 7 or just 7, common blade sizes are 9, 7, 5, 3, 1, 0, and 00. 9 being the heaviest and 00 very fine. blades are available from as high a number as 11 (10teeth per inch) right down to 00 (which are 27tpi).
I normally use the reverse...